PHP SQL, How do I query for the count of comments in a post (for blog posts)?

Question

I'm currently creating my own blog with a custom css built from scratch with PHP. I am still very new to the language and also with SQL. Right now I have a problem with displaying a Comments(3) link on each post that I query from the database. I have 3 tables: users, posts, and comments.

USERS

id | username | password | name | email | privileges

POSTS

postid | title | date | content | userid | visible | active 

COMMENTS

commentid | c_name | c_email | c_ website | c_date | c_content | approved | postid

This is my current query for displaying posts content from the db:

 $query = connect()->prepare(
    "SELECT * FROM posts JOIN users on posts.userid = users.id WHERE visible = 1 ORDER BY postid DESC");
$query->execute();

<div id="posts">
            <?php
               while($posts = $query->fetch(PDO::FETCH_ASSOC)) {
                $id = $posts['postid'];
                $title = $posts['title'];
                $date = $posts['date'];
                $content = $posts['content'];
                $name = $posts['name'];
            ?>
            <div id="entry" class="post-<?php echo $id; ?>">            
                <h1><?php echo "<a href='entry.php?id=".$id."'>" .$title. "</a>"; ?></h1>
                <div class="entry_content">
                    <?php echo $content; ?>
                    <p><span class="author"><?php echo $name; ?> on <?php echo $date;?></span></p>
                  //this is where I want to put the "Comments(3)"
                </div>
            </div>
            <?php } ?>
        </div>

I tried doing the below query to retrieve the number of comments by finding it by its post id INSILDE the while loop.

 <?php 
       $query = connect()->prepare("SELECT COUNT(postid) as commmentno FROM comments WHERE postid = :postid");
       $query->execute(array(':postid' => $id)); 
       $commentnos = $query->fetch();

       echo $commentnos['commentno'];
  ?>

But the results ended up that I only got one post displayed with the right number of comments... How do I get these results in one query?

Answer 1

A single query could work like:

SELECT
    posts.id, posts.title, posts.date, posts.content, posts.name,
    (SELECT COUNT(postid) FROM comments WHERE postid = posts.id) as commmentno
FROM posts
JOIN users on posts.userid = users.id
WHERE visible = 1
ORDER BY postid DESC

Then the inner query is not necessary at all because the primary query returned the comment count as a field.

Answer 2

I believe you have used the same variable name $query for both fetching post data and comment number. When you are using the same variable name $query $query = connect()->prepare("SELECT COUNT(postid) as commmentno FROM comments WHERE postid = :postid"); it overwrites the previous query result. So that you have only one posted displayed with right comment number. Try change your codes to

<?php 
       $commentquery = connect()->prepare("SELECT COUNT(postid) as commmentno FROM comments WHERE postid = :postid");
       $commentquery->execute(array(':postid' => $id)); 
       $commentnos = $commentquery->fetch();

       echo $commentnos['commentno'];
  ?>

Answer 3

You can try this:

$query = connect()->prepare(
"SELECT * FROM posts JOIN users on posts.userid = users.id WHERE visible = 1 ORDER BY postid DESC");
$query->execute();

<div id="posts">
        <?php
           while($posts = $query->fetch(PDO::FETCH_ASSOC)) {
            $id = $posts['postid'];
            $title = $posts['title'];
            $date = $posts['date'];
            $content = $posts['content'];
            $name = $posts['name'];
        ?>
        <div id="entry" class="post-<?php echo $id; ?>">            
            <h1><?php echo "<a href='entry.php?id=".$id."'>" .$title. "</a>"; ?></h1>
            <div class="entry_content">
                <?php echo $content; ?>
                <p><span class="author"><?php echo $name; ?> on <?php echo $date;?></span></p>
              //this is where I want to put the "Comments(3)"
             $cquery = connect()->prepare("SELECT COUNT(commentid) as commentno FROM comments WHERE postid='".$id."'");
             $cquery->execute();
             $result = $cquery->fetch(PDO::FETCH_ASSOC);
             echo $result['commentno'];
            </div>
        </div>
        <?php } ?>
    </div>